The present invention relates to an illumination device for simulating neon or similar lighting, and more particularly, to an illumination device incorporating a slotted and reflective circuit board to increase light-collection efficiency.
Neon lighting, which is produced by the electrical stimulation of the electrons in the low-pressure neon gas-filled glass tube, has been a main stay in advertising and for signage. A characteristic of neon lighting is that the tubing encompassing the gas has an even glow over its entire length irrespective of the viewing angle. This characteristic makes neon lighting adaptable for many advertising applications, including script writing and designs, because the glass tubing can be fabricated into curved and twisted configurations simulating script writing and intricate designs. The even glow of neon lighting being typically devoid of hot spots allows for advertising without visual and unsightly distractions. Thus, any illumination device that is developed to duplicate the effects of neon lighting must also have even light distribution over its length and about its circumference. Equally important, such lighting devices must have a brightness that is at least comparable to neon lighting. Further, since neon lighting is a well-established industry, a competitive lighting device must be lightweight and have superior “handleability” characteristics in order to make inroads into the neon lighting market. Neon lighting is also recognized as being fragile in nature. Because of the fragility and heavy weight, primarily due to its supporting infrastructure, neon lighting is expensive to package and ship. Moreover, it is extremely awkward to initially handle, install, and/or replace. Any lighting device that can provide those previously enumerated positive characteristics of neon lighting, while minimizing its size, weight, and handleability shortcomings, will provide for a significant advance in the lighting technology.
The recent introduction of lightweight and breakage resistant point light sources, as exemplified by high-intensity light-emitting diodes (LEDs), have shown great promise to those interested in illumination devices that may simulate neon or similar lighting and have stimulated much effort in that direction. However, the twin attributes of neon lighting, uniformity and brightness, have proven to be difficult obstacles to overcome as such attempts to simulate neon lighting have largely been stymied by the tradeoffs between light distribution to promote the uniformity and brightness.
In an attempt to address some of the shortcomings of neon, commonly assigned U.S. Pat. Nos. 6,592,238 and 6,953,262, which are incorporated in their entirety herein by reference, describe an illumination device comprising a profiled rod of material having waveguide properties that preferentially scatters light entering one surface (“light-receiving surface”) so that the resulting light intensity pattern emitted by another surface of the rod (“light-emitting surface”) is elongated along the length of the rod. A light source extends along and is positioned adjacent the light-receiving surface and spaced from the light-emitting surface a distance sufficient to create an elongated light intensity pattern with a major axis along the length of the rod and a minor axis that has a width that covers substantially the entire circumferential width of the light-emitting surface. In one preferred arrangement, the light source is a string of point light sources spaced a distance apart sufficient to permit the mapping of the light emitted by each point light source into the rod so as to create elongated and overlapping light intensity patterns along the light-emitting surface and circumferentially about the surface so that the collective light intensity pattern is perceived as being uniform over the entire light-emitting surface.
One of the features of the illumination device described and claimed in U.S. Pat. Nos. 6,592,238 and 6,953,262 is the uniformity and intensity of the light emitted by the illumination device. While it is important that the disadvantages of neon lighting be avoided (for example, weight and fragility), an illumination device would have little commercial or practical value if the proper light uniformity and intensity could not be obtained. This objective is achieved primarily through the use of a “leaky” waveguide rod. A “leaky” waveguide rod is structural member that functions both as an optical waveguide and light-scattering member. As a waveguide, it tends to preferentially direct light entering the waveguide, including the light entering a surface thereof, along the axial direction of the waveguide, while as a light scattering member, it urges the light out of an opposite surface of the waveguide. As a result, what is visually perceived is an elongated light pattern being emitted along the light-emitting surface of the waveguide rod.
As described in U.S. Pat. Nos. 6,592,238 and 6,953,262, a circuit board is typically populated with LEDs and placed in a housing adjacent the light-receiving surface of the “leaky” waveguide rod. The housing generally comprises a pair of side walls defining an open-ended channel that extends substantially the length of the rod. As such, the housing preferably not only functions to house the circuit board populated with the plurality of LEDs, but also to collect light not emitted directly into the light-receiving surface and reflect it into the rod. Thus, the internal surfaces of the side walls and the circuit board may be constructed of or coated with light-reflecting material (e.g., white paint) in order to increase the light-collection efficiency by reflecting the light incident upon the internal surfaces of the housing to the rod. However, constructing or coating the side walls with light-reflecting material can increase manufacturing costs. Accordingly, there remains a need for a construction for an illumination device which achieves the desired light-collection efficiency, but without unduly increasing manufacturing costs.